I can't flip my pose for my animation?
I guess your problem is a mix of wrong names and bad orientations.

You say that you tried to rename your bones, but in your file they are not properly renamed. The left foot must be named something like foot_L, and right foot something like foot_R, otherwise when you'll flip the pose, Blender won't be able to understand to what bone it is supposed to paste.

So when you have finished a side of your armature you should properly name all your bones, then, in Edit mode, select them all and Armature > Symmetrize so that it copy paste on the other side.

Also, you'll probably need to correct the rotation of the lower leg due to the IK: Once in Pose mode, select the lower leg, go into the Properties panel > Bone Constraints, play with Pole Angle value to correct the orientation.